Pick up a good mechanical oil pressure gauge. You can hook it up and not make a permanent fixture in your car if you need to. You could hook it and mount it under hood to check what it is at idle and with the engine running thru the RPM band. Good mechanical gauges are not expensive and are a direct piece that will read regardless of whether there is a circuit problem going to the electric. Your sender pulls a signal from there it sends it to the circuit board in your dash panel.